Mixed phase, alpha-beta titanium alloys and method for making same



STRESS, 1,000 P51 March 7, 1961 M B I .VORDAHL 2 9 MIXED PHASE, ALPHA-BETA TITANIUM ALLOYS 74076 AND METHOD FOR MAKING SAME Filed June 10. 1954 5 Sheets-Sheet 2 ULTIMATE STRENGTH v.5. ELo/vaAT/o/v FOR 77- 7 MN ALLo); QUENCHED neon BELOW BETA TEA/V305 AND AGED AT VARIOUS TEMPEEATuREs AND TIMES LEGEa/D FOE PLOTS.- SOLID 001::- As WATER .QUENCHED C/ecLEs ((A5 WATER QUENCHED AND AGED,

II ELONGATlO/V, 7! //v I IN V EN TOR.

MLTo/v B. VORDAHL.

BY I

MMMQWGuZLMM ATTOENEb'.

ULTIMATE STRENGTH, 7000 PSI March 7, 1961 M. B. VORDAHL 2,974,076

MIXED PHASE, ALPHABETA TITANIUM ALLOYS AND METHOD FOR MAKING SAME Flled June 10. 1954 5 Sheets-Sheet 3 ULTIMATE STRENGTH VJ. ELONGATION FOR VARIOUS MIXED PHASE, ALPHA-0E7?! TITANIUM BASE ALLOYS A5 QUENCHED FKOM ABOVE BETA TR/INJUS TEMPERATURE AND THEEEAF'TEE AGED BELOW BETA TRANSUS Lo/vaAr/0/v Z IN V EN TOR. ML'roN B. VbED/IHL.

WWW M621 ATTORNEYS.

ULTIMATE STRENGTH, 1,000 Psi March 7, 1961 Filed June 10. 1954 M. B. VORDAHL MIXED PHASE, ALPHA-BETA TITANIUM ALLOYS AND METHOD FOR MAKING SAME 5 Sheets-Sheet 4 ULTIMATE STRENGTH V3. ELONGAT/ON FOE VARIOUS MIXED PHASE, ALPHA BETA TITA NIUM BASE A LLOYJ A5 QUENCHED FROM BELO W BETA TEA NSUS TEMPERA TUEE AND THERE/1 F'TEE AGED.

[Lo NGA r1 01v INVENTOR. M1. TON B. Venom-l1.

A TTORNEYS.

March 7, 1961 M. B. VORDAHL 2,974,076

MIXED PHASE, ALPHA-BETA TITANIUM ALLOYS AND METHOD FOR MAKI Filed June 10. 1954 NG SAME 5 Sheets-Sheet 5 BETA TEANSUS TEMPERATURE VS. ALLOY CONTENT FOE VARIOUS TITANIUM BASE BINARY ALLOY SY STEMS WEIGHT PERCENT ALLOY INVENTOR. MLTo/v B I/OEDAHL.

ATTORNEYS.

Unite States Patent lVIIXED PHASE, ALPHA-BETA TITANIUM ALLOYS AND METHOD FOR MAKING SAME Milton B. Vordahl, Beaver, Pa., assignor, by mesne assignments, to Crucible Steel Company of. America, Borough of Flemington, N.J., a corporation of New Jersey Filed June 10, 1954, Ser. No. 435,754

'12 Claims. (Cl.

This invention pertains to methods of heat treatingtitanium base alloys having a mixed alpha-beta microstructure for imparting thereto exceptionally high strength binations of strength and ductility, and high ductilityat any given strength level, said methods consisting essentially in subjecting such alloys to prolonged plastic deformation at temperature within the miXedYalpha-beta temperature range, i.e., at temperature below the beta transus temperature at which the microstructure of these alloys. converts from mixed alpha-beta to all beta on heating. As set forth in said applications, the preferred temperature range for carrying out said plastic deforma tion extends from about 400 C. or 750 F. up to not more than about 50 C. or 100 F. below the beta transus temperature.

As shown in said applications, the efi'ect of plastically deforming such mixed phase alloys within the two phase temperature field, is to impart. thereto a microstructure comprising a coherent admixture or interleaved dispersion of small bodies ofalphatitanium and of. beta titanium. Since the alpha phase of' titanium is relatively weak and ductile, while the beta phase is relatively strong but less ductile, the result of this: interleaving and dispersion of the two phases is to impart uniformly throughout the alloy a combination of high-strength and high ductility.

The field of utility of the processes described in said applications is, however, restricted to conditions of fabri cation wherein the alloys can be; plastically deformed to the extent required for imparting the aforesaid microstructure, such, for example, as rolling into sheet or rod or drawing into wire, etc. Where, however, such alloys 2,974,076 Patented Mar. 7, 1961 invention applicable to titanium base alloys having a mixed alpha-beta. microstructure, consists in quenching such alloys from a temperature substantially below, i.e., at least 50-100 F. below, the beta transus temperature of the alloy, and thereupon subjecting the alloy to an aging treatment and preferably to a prolonged aging heat treatment at a somewhat lower temperature. Broadly' stated, the quenching temperature. range will extend from about 50 F. below the. beta transus temperature down to about 400 F. below the beta transus, a more preferred range extending from about 150 to 300 below the beta transus temperature, but in no instance is the. quenching carried out at a temperature below about 1100" F. The subsequent aging treatment is carried out within a temperature range broadly stated of about 7501000 P. for a period of about 1 to 50 hours, a more preferred aging procedure being to age the alloys after quenching, within the temperature range of about 800-900 F. for a period of about 2, to 12 hours.

In order to render the subcritical temperature quenchingitreatrnent of the invention most effective in strengthening the alloy, the heat treatment must consist in two main steps, first obtaining a good distribution or interdispersion of the alpha and beta phases, and secondly quenching in such manner as not to destroy the good alpha to beta distribution obtained by the preceding: step.

The first step can, of course, be carried out by th procedure outlined in my above mentioned earlier applications, i.e., by plastic deformation of'the alloy at temperature Within the two phase field. Particularly. good dispersions are thus obtained. with-the alpha and.

2 beta particles elongated and interleaved as results, for" example, by rolling or drawing, since this results in greateristrength in the direction ofthe applied stress.

An advantage of securing a good dispersi'onof the alpha and beta phases by plastic, deformation in the two phase field, is that the history of the alloy prior to such plastic deformation is of little, if any, significance. The efiect of the plastic deformation in the two. phase field 1s toincrease the ductility at a given strengthlevel and this eifect is quiteindependent of the prior history or prior heat treatment of the alloy. Whether the alloy has been hardened by quenching from the beta field or from a lower temperature, or has been previously fully annealed, as byslow' eooling from a beta field temperature, or given any other treatment, extensive working in the twophase. field still develops the optimum proper- I prior to subjectingthe sameto the quench, hardening heat treatment of the present invention. A good example.

temperature, i.e.,; from a temperature at which the alloyw tion. Accordingly, a primary objectof the present invention is to provide methods of: so heat treating such alloys as to duplicate or surpass the strength. and ductility prop erties impartabletheretoj by the t-wophase field, plastic,

deformation procedures of earlierapplications above mentioned.

Basically the; heatltreating processes .of the present .t e. at w i h t s al e se alternative for' securinga good alphato beta distributions? dendritic, growth,;more commonly. known as a Wedm of this is the case of massive forgings, requiring worlcing in the beta temperature field, in which case an acceptable 1 is obtained by slow cooling from above. the beta transus assumes an. all-betamicrostrueture. Such siow' 'coolingf' from above the betatransus temperaturq;precipitates the, alphaiphase. by a-.p r'ocess which may be 'termed Solid is, generally lamellar in character.

p The conventional practice for quench hardeningielloys in general is to quench from above. thecriti'cal terii s i sl sha structure. Thus, in the case of hardenable and temperable, martensitic steel, quench hardening is effected by quenching from the austenitizing temperature range, i.e., from above the temperature at which the steel converts from ferrite to austenite on heating. Depending on the rate of quenching and on the carbon content and the contents of other alloying elements present, any desired degree of hardening, within limits, may be thus obtained, and the hardness thereafter reduced to a desired degree with accompanying increase in ductility by subsequent tempering at a sub-critical temperature.

In the case of the mixed-phase alpha-beta titanium base alloys, however, quenching from above the beta transus temperature results in general in an extremely brittle alloy which cannot thereafter be transformed into a strong and ductile alloy by subsequent heat treatment at a temperature below the beta transus temperature.

In contrast, however, and by employment of the process of the present invention, wherein the alloy has first imparted thereto a good alpha-beta distribution as by plastic deformation in the alpha-beta field, or by slow cooling from the all-beta field, and thereafter quenching from a temperature below the beta transus temperature, there is imparted to the alloy an excellent combination of strength and ductility, all as substantiated by the comparative test data hereinafter presented. Applicant is aware of no other instance in metallurgy wherein it has been established as optimum to initiate hardening by quenching from within a two phase field rather than from a higher temperature single phase field; or wherein prior to quenching from within a two phase field, the two phases of the alloy are advantageously distributed, by either of the two procedures aforesaid, i.e., by prior plastic deformation in the two phase field, or by slow cooling from a higher temperature single phase field.

The following Table I shows the efifect on ultimate strength and tensile elongation of heat treating various mixed alpha-beta titanium base alloys by (a) quenching from above the beta transus temperature followed by aging or tempering at a temperature below the beta transus, and (b) quenching from below the-beta transus temperature followed by tempering or aging at a still lower temperature.

TABLE I Composition, Ultimate Elong Percent (Balance Treatment Titanium) (p s l Percent (a) 6M0 1,000 C. 15 min. quenched 161, 900 into water; tempered 800 F. a 6M 0:110 min.

0 o 188,800 2 E0; 6M0 850 15tmln. quench ed into 189 200 {5a. empered 800 F. for 190:800 4 (a) 6Mo-O.1N.. Quenched into water 10 mln. ggg: 8.; tempered 20 min. g 'ggg g 192: 200 a (o 6Mo-0.1N--.-. Quenchcd mm water 10 min. 3 gg: 8.; tempered 20 min. i 1981800 3 (a) 4Mn quenched into water min. 52 1 $30 080; tempered min. g 388 2 (b) om Gold rolled; quenched into 6 water for 15 min. 725 0.; 31300 5 tempered for 40 min. 450 o. 3' i% g fi'om below the beta transus temperature and thereafter,-

tempered.

The data in'Table I'are based on short time temper- 75 V f ing following quenching. Such heat treatment is desirable because of the ease with which it may be conducted. Furthermore, it results in an ideal microstructure in that the distribution of the two phases, i.e., alpha and beta, is ideal as far as strength and ductility are concerned. The microstructure consists of a beta phase matrix which contains a random distribution of globular alpha phase islands. No better distribution with respect to ductility is conceivable. The objection to this short time tempering treatment following tempering, however, is that it is not thermally stable. On long time exposure to moderately elevated temperatures, transformation takes place, due to further conversion of the retained beta into the alpha phase, so that the mechanical properties are consequently altered resulting in a decrease in ductility. Hence the material in this condition is not suitable for applications where elevated temperature service is encountered.

For imparting thermal stability, the mixed phase alloys as quenched from the alpha-beta field are, in accordance with a further aspect of the invention, subjected to an aging heat treatment in the temperature range of about 750-1000 F. and preferably, for optimum results, at about BOO-900 F. Although relatively short time aging up to about 1 hour or so substantially increases the thermal stability as compared to the as quenched condition, for imparting maximum thermal stability, prolonged aging or overaging is required. Thus, duration of the aging cycle may vary over a broad range of about 1 to 50 hours, a preferred aging cycle for good thermal stability being from 2 to 12 hours.

The data contained in the following Table II is illustrative of the results obtainable by application of the aforesaid heat treatment according to the invention, to a typical mixed phase, alpha-beta titanium base alloy containing about 6.5% manganese and the balance titanium of commercial purity. An ingot of this alloy as produced by are melting in a cold mold furnace in an inert or argon atmosphere, was hot rolled at 1300 F. and a series of test specimens prepared therefrom. Groups of these specimens were then heated for 2 hours at 1100 to 1500 F. in an inert atmosphere, and quenched in water to room temperature. Individual specimens were then aged at temperatures of 700-l000 F. for the periods indicated in the table, and tested for room temperature mechanical properties with results as set forth.

TABLE II Quenched and aged tensile properties on Ti6.5Mn alloy Tensile Properties Aging Aging a Time, hrs.

1,100 E, 2 hrs 5 Table Iii-Continued Quenchea' and aged: tensile properties on I Ti6.5Mn ailoy-Continued.

' Tensile Properties Aging Aging Water Quench, Temp., Time, 'Dnneandlemp. F. hrs. Ult. Y.S. EL, 11.11.,

(1,000 (1,000 Per- Perp.s.i.) p. .1.) cent cent 2 199. 6 186. 8 1.0 0.8 8 7 207.7 183.3 3.0 2.4 700 16 207.7 185.7 3.0 1.6 24 207. 7 184. 9 4. 1. 6 48 206.1 182.7 2.0 2.4 96 200. 4 178. 8 2. 0 2. 4 1 195. 173. 9 8.0 7. 9 4 191. 4 161. 1 9.0 17.1 800 8 186.0 154. 6 13.0 29. 4 16 182. 5 156.7 16.0 37.9 I a 121-: as 1 8.2 L309 12, 174.5 157.8 15.0 39.2 1 2 166. 0 151.4 17.0 48.3 900 8 158.8 145.8 18.0 52.5 16 155.6 142.4 i 21.0 48.1 32 150.7 141.4 I 23.11 48.3 64 145. 0 136.3 24. 0 57. 0 167.2 153.2 21. 0v 49.3. 162.7 150. 5 21. 0 v 49.5 1 000 1 156.4 14319 21.0 I 52.5 2 1564 148.1 22. 0. 53.2 6 149. 3 141. 5 23.0 54. 7 24 141. 0 135. 2 23.0 54.1 2 7 16 1 215.9 2.0 1.6 4 2106 1.0 .8 800 s- 214.1 188.3 5.0 4.8 16 206.9 191.4. I 10.0 I 18.9 48 196. 0 177.0 10.0 26.7. 96 188.1 175.4 13.0 2970 A 201.2 185.1 7.0 13.1 1,400 F., 211118 2 185. 7 171. 5 11.0 34.8 900 8- 177.2 163.9 I 12.0 24.6 16 168.4 158.5 15.0 32,3 32 162.1 150.9 18.0 v 39.1 64 153. 0 141. 8 25. 0 '54. 0 $4 182. 6 171.5 12. 0 27. 3 A 177. 8 166. 1 16. 0 48. 7 1 000 1 172.1 160.9 17.0 48.1 2 165. 7 153. 5 17. 0 43. 8 6 153.5 143.4 20.0 43.2 24 146. 6 136. 5 20. 0 43. 4

1 5 2 4 (9 16 197.6 48 229.7 227.8 3.0 1.6 96 216.4 211.5 Y 3.0 5.5 $6 230. 3 227. 4 1. 0 1. 6 1,500 11.,2hrs 2 220. 0, 211.1 3.0 5.5 900 8 202. 5 191. 1 4. 0 6. 4 16 190. 7 183. 9 5.0 13. 1 32 180. 2 177.9 7.0 13.8 64 171.1 165. 2- 7. 0 16.9 54 203. 7 196. 3 3. 0 7. 9 202.4 194. 1 4. 0 7. 1 1 193,1 182.9 4.0 9.3 2 179. 2 171'. 9 6. 0 16. 1 16.5.6. 159.2 7. 0 18. 4: 24 151.9 144.6 14.0 g 31.4

the beta-to-alpha transformation occurs too rapidlyfor convenient control. The best quenched and aged properties are obtained by quenching in the vicinity of 1400 R, which, for this alloy, is about 150 below the beta transu's, and thereafter aging at abouti800 10900" F.

Tensile strengths up to 200,000 p.s.i. with 10% elongationare obtainable by thistreatment, as shown bythe data. This alloy as quenched in water after 2 hours at 1 400 F, had the following properties: 'ulti'rnate'st'rength' 177,000- p.s.i;, yield strength 171,800 p.s.i.,' elongation 1 5%, reduction in area 32.4%.

Various ot'the Table 11 .quenchedandl aged conditions were also investigated for-notch sensitivity of this alloy.

For these tests, standard one-fourth inch notched. tensile specimens were employed. The notched ultimate vs. plain ultimate ratios observed on these specimens are given in the following Table III, together with the ultimate strength and reduction in area for the plain and notched specimens. This data shows that the alloyin the quench-averaged condition is not notch sensitive at stress concentration up to 3.4.

TABLE III I Notched tensile properties on heat treated Ti6.5Mn alloy p.s.i.X1,000 1 Red. in Area, Percent N Ult./ Condition Ult. Strength P Ult.

. Ratio :Plain' Notched Plain Notched v 2 hrs. 1,300 F., 11 0 Q+8 hrs. at 800 F 186. 0. 238.1 29.4 5.0 1.28 2 hrs. 1,100 F., H O

+1 6 hrs. at 800 F 206.9 249.0 18.9' 7.4 1.21 251.7 34. 8v 8.7 1:35 248.4 32.3 11.8 1. 49 252.4 27.3 3 53; 1. 33 248;.2 48.7 8.1 1 1.40

. 230.0 6.4 728 1 1.13 235.9 13.1 8.7 x 1.23 +32hrs. at 900! 180.2 227.2 13.8 8 23 1526 Table IV below gives the res'ultsof a series of quenching and aging tests on a mixed phase,-alpha-beta" alloy contai-ning'about 4% aluminum, 4% manganese andthe balance titanium of commercial purity. These testswere conducted in the same manner as those for the above Table II. The beta transus temperature for this alloy is about 1700 F. i

TABLE IV' V Quenchea and aged tensile properties of. Ti4Al4Mn I alloy Tensile Properties I Aging Aging Water Quench, Temp, Time, Time and Temp. F; hrs. Ult. Y'.S. EL, R .A., '(1,000 (1,000 Per-f Pen. p.s.i.) p.s.i.) cent cent.

Y 2 158.7 148.7 20.0 7 46:5 700 16 162.9' "151.7; 16:0" 40.9. I (I .48. 167.7 153.8 12.0, 36.2 I g I v 2 160.9 148.4 17.0 44.0 800 16 188.2 157.1 710 9.3.? 1,3509 E.,2hrs; 48. I 189.8 165.8 13.0.. 27.5 7 I i -1- 163.5 151.4 15.0 4259 90,0; 16 183.3 162:3 13.0 '3124 I I .24 182.1 164.4 14.0, 30. 1 2' 165.6 150.8 13.0 36:2 1,000, 16 161.3 148. 6. 15.0' 3.9.7: 24- 161.5: 151.4 18.0. 156.1 149.1 21.0" I 42:5 I 2" 1 78.6 160.3 13.0 1428: 7% -15 215.9. 1.71.7 4.0 4.1. 21 205.7 168.5 2.0 1.11 I I 4s 167.7 153.8 12.0 36. 2 2 213. 8 170. 5 6. 0 10.2 .1 an 23-2 s-s o I I I :5. Ila45agF-izhrs 48 215.9 177.4 541 10,2

24 169.5 154.3 15.0 34. 4 156.9 150.5 17.0 'aaav Z. 13%.: 1 16 187.4 48 199. 2v 2 191.4 800 16 209.8 v p 48 215.9 1,55o r.,211r 900 8 216.5 16 209.9 24 196.3 1 215. 9 2 214.4 1,000. 4 203.7 1a .1696 24 177.6

7 Table IV-Continued Tensile Properties Aging Aging Water Quench, Temp., Time, Tlmeandlemp. F. hrs. Ult. Y.S. EL, R.A.,

(1,000 (1,000 Per- Perp. .i.) p.s.i.) cent cent 1,650 F.,2hrs

1,750 F.,2hrs

Brittle.

It will be seen from Table IV that the quenching and aging response of this Ti--4Al4Mn alloy is generally similar to that of the T i--6.5Mn alloy of Table II, except that optimum properties are in this instance obtained by quenching from about 1350-1450 F. and aging at about 900-1000 F. Here again, tensile strengths up to about 200,000 p.s.i. with accompanying elongation of about are obtained.

Referring now to the annexed drawings for a further description of the invention:

Figs. 1 to 5, inc., are photomicrographs showing the microstructure of a Ti7Mn, mixed phase, alpha-beta alloy after being subjected to various heat treatments according to the invention as discussed below.

Fig. 6 is a graph comparing the strength versus ductility of the Ti-7Mn alloy as quenched from the alphabeta field and also after subsequent aging.

Fig. 7 is a plot of tensile strength versus ductility of numerous specific analyses of mixed phase, alpha-beta alloys, as quenched from above the beta transus temperature; while Fig. 8 is a comparative plot of such alloys as quenched from below the beta transus temperature.

Fig. 9 is a plot showing the beta transus temperature versus alloy content for various binary alloys of titanium and a beta stabilizing element.

Referring to the photomicrographs Figs. 1 to 3, inc., show as quenched microstructures of the Ti-7Mn alloy as water quenched from 1375, 1425 and 1575 F., respectively. As shown by Fig. 9, the beta transus temperature of this alloy is about 780 C. or 1440" F. Thus Figs. 1 and 2 show the alloy as quenched from the alpha-beta field and Fig. 3 as quenched from the beta field. It will be noted that increasing quenching temperature results in decreasing amounts of alpha titanium (darker etching islands) in the beta titanium matrix (light background). This, as shown in the drawing, is accompanied by increasing tensile strength with decreasing ductility and increasing hardness, as measured on the Rockwell A scale and designated RA. It will further be noted that whereas quenching from the alpha-beta field gives combinations of high strength and ductility, quenching from the beta field rendered the alloy glass brittle.

Figs. 4 and 5 illustrate the aging response Pattern of specimens of the alloy as air cooled in one instance from 1425 F. and aged 4 hours at 600 F, Fig. 4, and as air cooled from 1425 F.'in the other instance and aged 4 hours at 800 E, Fig. 5. Note that the Fig. 4 structure is glass brittle and quite hard, RA 73.6. This material has been aged but not overaged. The structure of Fig. 5, on the other hand, has been aged at a higher temperature and is in the overaging condition as indicated by the dark etching background. The dark etching background is the result of a very fine dispersion of transformed alpha titanium in the.beta titanium matrix, the white etching 8 islands being the alpha titanium present prior to aging. As a result of this overaging, it will be noted that the Fig. 5 structure has regained considerable ductility and is much softer than the Fig. 4 structure.

Referring to Fig. 6, the solid dots are plots of ultimate strength versus tensile elongation for quenched specimens of the Ti7Mn alloy as quenched from various temperatures in the alpha-beta field; while the circles are similar plots of this alloy as quenched from variousalpha beta field temperatures and subsequently aged at varying temperatures and times. The purpose of the plot is to show that the as quenched mechanical properties can be duplicated in the quenched and aged specimens as regards any desired combination of strength and ductility. This is of prime importance because, as shown above, the distribution of the alpha and beta phases in the alloy as quenched from the alpha-beta field, is ideal as regards strength and ductility. Hence the ability to duplicate these as quenched properties in the alloys as quenched and aged, results in the attainment of maximum strengthductility combinations combined with high thermal stability.

As shown above in Table I for various typical mixed alpha-beta alloys, quenching from the beta field in general renders the alloys weak and brittle; whereas quenching from the alpha-beta field results in general in greatly increased strength with retention of good ductility. That these observations are rules of general application is shown by the test results plotted in Figs. 7 and 8.

In Fig. 7 is plotted ultimate strengths versus percent tensile elongations for numerous mixed alpha-beta alloys as heat treated in the beta field and quenched. Test results are given for such alloys containing about 2 to 15 atomic percent of one or more of Mo, Mn, Cr, Fe. Fig. 8 is a similar plot of such alloys as heat treated in the alpha-beta field and quenched.

It will be seen from the envelope curves A, Fig. 7, and B-B, Fig. 8, that for any given ductility, the strength level is much higher for these alloys as heat treated in the alpha-beta field than when treated in the beta field. Based on data similar to Figs. 7 and 8 for the Ti-7Mn and Ti-4Al4Mn alloys, the advantage of heat treating in the alpha-beta field as compared to heat treating in the beta field prior to aging or overaging is shown by the following:

Attalnable attainable Strength Level Alphapercent wai -E18 It will be seen from the above data that at any given strength level, greater ductility is secured by heat treating the alloy in the alpha-beta field in accordance with the present invention, i.e., by quenching from below the beta transus temperature followed by aging, than is obtainable by quenching from above the beta transus temperature followed by aging.

Although best results are generally obtainable by rapid quenching of the alloys from below the beta transus temperature, as by quenching into water, other quenching media may be employed such as oil quenching and even cooling in air, the latter as shown by some of the examples above discussed.

Referring' to Fig. '9 there is shown a plot of the beta transus temperature versus alloy content for titanium '9 meter additions have been published in the literature. The beta transus temperature for any particular alioy may be determined by quenching specimens from progressively higher temperatures, until a completely martensitic or retained beta microstructure is obtained.

The heat treatment process of the invention is applicable in general to titanium base alloys having. a mixed alpha-beta microstructure. Such alloys are generally those containing about are 15 atomic percent of one or more beta promoters. In such alloys the .isomorphous beta promoters, molybdenum, vanadium, columbium and tantalum may be present singly or in aggregate up to the upper limit of about 15 atomic percent. The same is also true of the sluggishly eutectoid beta promoters chromium and tungsten. Manganese may be present up to about 10 percent by weight and iron up to about 7 percent by weight, consistent with the retention of adequate ductility in the alloy. The rapidly eutectoid beta promoters cobalt, nickel and copper may be present up to about percent by Weight singly or in aggregate. For all such additions, the lower effective limit is about 0.5% and preferably about 1% by weight.

The mixed phase alloys to which the invention is applicable may also contain one or more of the alpha promoters, the more important of which are, aluminum up to about 8 percent by weight, tin up to about 23 percent by weight, and antimony up to about 18 percent by weight, for the ductile alloy range. Here again, the lower effective limit for these additions is about 0.5 percent and preferably about 1 percent by weight, singly or in aggregate.

The interstitials carbon, oxygen and nitrogen, which also function as alpha promoters, should not be present in these alloys in amount exceeding about 0.2 percent each by weight.

It was pointed out at the outset that for securing a good alpha-beta distribution, plastic deformation in the alpha-beta field cannot always be resorted to, as for example in the case of massive forgings, and that in such cases the distribution is alternatively obtained by slow cooling from above the beta transus temperature, an appropriate cooling rate being about 250 F. per hour.

Even in the case of products formed of rolled sheet or rod or drawn wire, which as rolled and/or drawn in the alpha-beta temperature range, has a good alpha-beta distribution, it is frequently not possible to use the material in the as rolled or drawn condition, owing to fabrication operations to which this semi-finished product must, in many instances, be subjected, such, for example, as blanking, punching and forming operations. It is often necessary that such rolled or drawn material have considerably lower properties for these operations than are required in the finished articles. The material must, therefore, be converted to the annealed condition for the final finishing operations as by slow cooling from the beta field, in which case'it must thereafter be hardened and strengthened, this being accomplished by quenching from below the beta transus temperature and subsequently aging in accordance with the heat treatment of the invention herein.

What is claimed is:

1. The method of strengthening a titanium base alloy having a mixed alpha-beta microstructure which comprises: heating said alloy to a temperature within the range of'about 50 to 400 FJbelow the'betatransus temperature, and thereupon rapidly cooling substantially to room temperature. I i f 2. The method of strengthening a titanium base alloy having a mixed alpha-beta microstructure which come perature within the range of about 50 to 400 below:

the beta transus temperature and rapidly cooling, and thereupon aging at a temperature of about 750 to 1000" F. for about 1 to 50 hours 4. The method of strengthening and thermally stabiliz ing a titanium'base alloy having a mixed alpha-beta micro: structure,which comprises: heating said alloy to a remperature within therange of about 50 to 400 F. below the beta transus temperature and rapidly cooling, and thereuponaging at a temperature of about 800" to 900 F. for about 2' to 12 hours."

5. The method of strengthening and thermally stabilizing a titanium basealloy'ha'ving'a mixed alpha-beta microstructure which comprises: heating said alloy to a temperature of about 1300 to 1450 F. and rapidly cooling, and thereupon aging at about 800 to 900 F.

6. The method of strengthening a titanium base alloy having a mixed alpha-beta microstructure, and without unduly embrittling the same, which comprises: plastically deforming said allow at a temperature below the beta transus temperature, thereupon heating to a temperature within the range of about 50 to 400 F. below said beta transus temperature and rapidly cooling substantially to room temperature.

7. The method of strengthening and thermally stabilizing a titanium base alloy having a mixed alpha-beta microstructure, and without unduly embrittling the same, which comprises: plastically deforming the alloy at a temperature below the beta transus temperature, thereupon soaking at a temperature within the range of about 50 to 400 F. below the beta transus temperature and rapidly cooling, and thereupon aging at a temperature of about 750 to 1000 F. for about 1 to 50 hours.

8. The method of strengthening and thermally stabilizing a titanium base alloy having a mixed alpha-beta micro structure, and without unduly embrittling the same, which comprises: heating said alloy to a temperature above the beta transus temperature and slowly cooling to a temperature, below the beta transus, thereupon soaking at a temperature within the range of about 50 to 400 F. below said beta transus, and rapidly cooling substantially to room temperature.

9. The method of strengthening and thermally stabilizing a titanium base alloy having a mixed alpha-beta microstructure, and without unduly embrittling the same, which comprises heating said alloy to a temperature above the 7 beta transus temperature and slowly cooling to a temperature below the beta transus, sufficiently slowly to im: part a lamellar structure, thereupon soaking at a temperav ture within the range of about 50 to 400 F. below said beta transus and rapidly cooling, and thereupon aging at a 1 temperature of about 750 to 1000 F. for about 1 to 5 hours. I p Y 10. The method of strengthening a titaniumfbase alloy 1 having a mixed alpha-beta microstructure which corn-l prises: heating said alloy to a temperaturebelow the beta transus temperature but not less than about 1100" F., and thereupon rapidly cooling substantially to room tempera;

ture. i

11. The method of strengthening and thermally stabiliz ing a titanium basealloyhaving a mixed alpha-beta'miero structure, butwithout' unduly embrittling the same, which 'and rapidly cooling, and thereupon aging ata temperatureof about750 to 1000 F. for about 1 to 50 hours. 12.;The'method of strengthening and thermally stabiliz H ing a titanium base alloy having a mixedalpha-beta microstructure but without unduly embrittling thje"same,whic 'comprises: plastically deforming the alloy at a tempera cooling substantially perature for imparting a fine grained in'terspersion of ,the

beta transusrtemperaturebut not less thanaboutlIQO? F., I

ture ofaboutlOO to 7 50 nbuow the beta transus tern alpha and beta phases,thereupon'soakingat' a tempera ture within the rangeof about to 300 Rbelow'i sa id '11 '12 beta transus and rapidly cooling, and thereupon aging at 2,769,707 Vordahl Nov. 6, 1956 2,821,475 Jaffee et al. Jan. 28, 1958 about 800 to 900 F. for about 2' to 12 hours.

8 References Cited in the file of this patent OTHER REFERENCES UNITED STATES PATENTS Titanium Project, Navy Contract No. NOa(s) 8698 Gel-Her July 2 1940 Report No. 10, Feb. 16, 1948, pages 1, 3-9, 11-14. jafie et 1, May 22 1951 Titanium Project, Navy Contract No. NOa(s) 8698 J fiee Man 4 1952 Report No. 13, Apr. 9, 1948, pages 3, 4 and 5.

Herres et a1. July 14, 1953 Titanium Project, Navy Contract NOa(s) 8698 Report Craighead Dec.29, 1953 No. 14, May 11, 1948,'P. R. Mallory and Co., Inc.,

Vordahl Apr. 13, 1954 page 6.

Vordahl Mar. 15, 1955 Zeitschrift fiir Metallkunde, vol. 29 (1937), pages 190, 191.

Jafiee July 10, 1956 

1. THE METHOD OF STRENGTHENING A TITANIUM BASE ALLOY HAVING A MIXED ALPHA-BETA MICROSTRUCTURE WHICH COMPRISES: HEATING SAID ALLOY TO A TEMPERATURE WITHIN THE RANGE OF ABOUT 50* TO 400*F. BELOW THE BETA TRANSUS TEMPERATURE, AND THEREUPON RAPIDLY COOLING SUBSTANTIALLY TO ROOM TEMPERATURE.
 12. THE METHOD OF STRENGTHENIN AND THERMALLY STABILIZING A TITANIUM BASE ALLOY HAVING A MIXED ALPHA-BETA MICROSTRUCTURE BUT WITHOUT UNDULY EMBRITTLING THE SAME, WHICH COMPRISES: PLASTICALLY DEFORMING THE ALLOY AT A TEMPERATURE OF ABOUT 100 TO 750*F. BELOW THE BETA TRANSUS TEMPERATURE OF IMPARTING A FINE GRAINED INTERPERSION OF THE ALPHA AND BETA PHASE, THEREUPON SOAKING AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 150* TO 300*F. BELOW SAID BETA TRANSUS AND RAPIDILY COOLING, AND THEREUPON AGING AT ABOUT 8000* TO 900*F. FOR ABOUT 2 TO 12 HOURS. 